Biophysical studies are planned on human and procine neurotubule assembly and disassembly. Kinetics will be characterized in vitro by electron microscopy and optical measurements to ascertain the important factors involved in the control and mechanism of assembly. Assembly and disassembly of paired hellical filaments, which have been found only in the abnormal human brain, will be studied using protein isolated from autopsied brain from patients with senile dementia, Alzheimer's disease or Guam-Parkinsonism dementia. Major goals are to understand the mechanism of action of colchicine and vinblastine on microtubules, the possible regulatory role of Ca++ and Mg++ on microtubule assembly and the difference between neurotubules and paired helical filaments. BIBLIOGRAPHIC REFERENCES: Gaskin, F.; Litman, D.J.; Cantor, C.R.; and Shelanski, M. L.: The Formation of Filamentous Structures From Iodinated Neurotubules. J. Supramolecular Structure 3,39-50 (1975).